Tablet interacts with magnets, how does that work?

Making computers interact with physical objects is a favorite of the HCI gurus out there, but these builds usually take the form of image recognition of barcodes or colors. Of course there are new near field communication builds coming down the pipe, but [Andrea Bianchi] has figured out an easier way to provide a physical bridge between computer and user. He’s using magnets to interact with a tablet, and his idea opens up a lot of ideas for future tangible interfaces.

Many tablets currently on the market have a very high-resolution, low latency magnetometer meant for geomagnetic field detection. Yes, it’s basically a compass but Android allows for the detection of magnets, and conveniently provides the orientation and magnitude of magnets around a tablet.

[Andrea] came up with a few different interfaces using magnets. The first is just a magnets of varying strengths embedded into some polymer clay. When these colorful magnetic cubes are placed on the tablet, [Andrea]’s app is able to differentiate between small, medium, and large magnets.

There are a few more things [Andrea]’s app can do; by placing two magnets on an ‘arrow’ token, the app can detect the direction in which the arrow is pointing. It’s a very cool project that borders on genius with its simplicity.

But when you look inside a hard drive, you’ll find quite a strong neodymium magnet, which is used for the positioning of the read/write head, right next to the actual disc.
If this strong magnetic field doesn’t delete the information stored on the disk, then a little magnetic field coming from outside the harddrive might not cause any trouble.

That old BS again, no neither RAM not HD’s are affected by normal magnets, not even the neodymium ones. (who came up with it ever affecting RAM is beyond me, must be from the time when they used magnetic coil memory 50 years ago.)

But there might be a small issue, the sensitive compass devices might lose calibration maybe if exposed a lot to a powerful magnet?

If the mobile devices have magnetometers sensitive enough to sense the earths magnetic field, how much abuse are they being put through when the magnets he displays are 4 and 5 orders of magnitude stronger?

The magnetometer itself does not have a problem with fields of this strength. The big concern is if you magnetize a ferrous component of the tablet. If this happens you can build a degaussing coil to fix it, however its unlikely that there would be a significant amount of ferrous material in there since that would affect the normal operation of the compass as well.

Certain devices such as Garmin GPS units have a compass calibration mode where you rotate the compass around so it can determine the magnetic field bias from magnetized ferrous components and mathematically compensate for it. I do not believe any of the tablets do this yet.

I didn’t have the time to look up what type of sensor mobile devices used. So I wasn’t sure if there was a max/min range that the sensor could work in.
It seems the bulk of these are magnetoresistive(honeywell AN-203 for apple products) so you just lose accuracy once you’re outside the range they’re calibrated for.

@Dmitry
I’m admitedly ignorant on the subject, but how does magnetizing a part of the chassis ruin the device forever? Assuming you know that it’s off, why can’t you A) degauss as has been suggested B) recalibrate using the software function that seems to be available in most devices?
A third option outside the comfort zone of many would be to calibrate it the old fashion way as one does for shipboard compasses. I’m sure some creative dremeling or addition of small magnets would get you calibrated but take most of an afternoon.
So I guess my question boils down to this: The sensor itself isn’t broken or less accurate, it just doesn’t know it’s not oriented correctly so why can’t you adjust it through the software?

It may just be that they could do a better job of removing ferrous materials from the tablet. I don’t have any right now but I suspect the AA batteries used in my garmin gps are ferrous. Also it may be that the watch battery in your watch is ferrous. Lithium batteries may not be.

This is *incredibly* bad for your device – you can easily ruin forever its ability to sense earth’s field if you magnetize even a small component inside… A degaussing coil may not help much, since the tablets are initially *somewhat* magnetized by the internal speaker magnets and such. This is why they are very precisely calibrated…Even after your degaussing you may end up with a compass that is off…

Furthermore, by ruining the sensitivity of internal compass, you may ruin other things, which use sensor fusion (using mag, accel, and gyro together to get stable heading data). If your compass is not working well, it will not compensate for gyro drift well, ruining some AR apps and some games

For years, I kept my Motorola Droid stuck to the dash of my work truck with a half-dozen or so small neodymium magnets and a small sliver of steel stuck to the battery door. No ill effects, other than the added steel becoming slightly magnetic.

As to “precise calibration”: This device didn’t have any meaningful factory calibration from day one, often being off by 30 degrees or more.

Instead, to calibrate: Turn on the compass, hold it in your hand, and give it a few iterations of a figure-8 while being well away from other ferrous objects. Viola: A reasonably accurate compass, at least for the duration — even with the magnetized chunk of metal on the back.

It may also be worth noting that this particular phone uses magnets in its various docks to set the state of things.

And I’d also like to point out that various newer tablets have OEM covers with magnetic closures.

And so, please allow me to assign a value of 0 on the Fearmonger scale for combinations of magnets and tablets: It doesn’t seem worth worrying about.

I put my brand new Samsung galaxy tablet 8.9 in a case with a magnetic clasp.
Magnetic sensors are now ruined. Been trying to recalibrate and find
a solution for several days now, to no avail… AVOID LONG TERM MAGNET EXPOSURE!!!